Light emitting diode (“LED”) devices usually show low consumption of electrical power, low heat generation as well as a long lifetime and small volume. Due to these characteristics, LED devices are recently used as a light source in various lighting applications.
LED devices usually include LED dice mounted on a substrate. Such LED dice generally include a structure of stacked layers including various semiconductor layers enabling the LED die to emit light in a specific wavelength range resulting in a specific color of the emitted light depending on the used materials. Examples for such LED dice with a structure of stacked layers are described for example in U.S. Pat. No. 6,650,044 B1 and in U.S. Pat. No. 7,049,159 B2. Since such an LED die does not naturally emit white light, a phosphor material is usually applied to the LED die in order to adjust the color of the emitted light such that the light appears as substantially white light to the human eye.
Further, in order to distribute the light emitted by the LED die in a desired manner, LED devices may be additionally provided with a white reflector layer. A method for manufacturing an LED device with a reflector layer is described in U.S. Pat. No. 8,921,131 B2.
The conventional approaches for forming a phosphor layer and a reflector layer usually use molding techniques, such as injection molding or transfer molding as described in U.S. Pat. No. 8,921,131 B2, or dispensing/spraying techniques, such as using a nozzle to dispense the reflector material or spraying the phosphor material onto the LED die. However, these approaches typically are not sufficiently precise and require post-processing, such as grinding the material layer formed by molding to a desired final thickness. These additional processes make the conventional approaches slow and impose a risk of damaging the LED die during grinding. Further, additional and expensive special-purpose equipment, such as machines for molding, spraying and post-processing, is required and grinding increases the waste of the used materials, thus increasing production costs. In addition, the conventional approaches cannot control the sharpness of printed layer edges to a sufficient degree and suffer from the effect of surface tension due to the liquid nature of the liquid materials used for forming the phosphor layer and the reflector layer prior to their solidification and thus the formation of a meniscus such that the flatness of the surfaces cannot be sufficiently well controlled.